This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 11-148239, filed May 27, 1999, the entire contents of which are incorporated herein by reference.
The present invention relates to a focus detector to be used for a camera or the like, and more particularly to a focus detector that is used for an image pick-up device.
There have so far been proposed a large number of focus detectors. Each of these focus detectors is designed to guide an image formed by an image pick-up lens onto a focus detection optical system, split the image into two piece of images, form these images again on photoelectric conversion elements, and detect positional deviations between the two images that have been formed on the photoelectric conversion elements, thereby to detect the focus of the image picked-up object.
For example, Jpn. Pat. Appln. KOKAI Publication No. 10-104502 discloses a focus detector that expands a focus detection area. The focus detector described in this publication uses an exclusive focus-detection area sensor.
According to the technique described in Jpn. Pat. Appln. KOKAI Publication No. 10-104502, however, the exclusive focus-detection area sensor is used, and the cost thereof is increased. Therefore, there is a problem that it is not practicable to mount such an expensive focus detector onto a low-price camera.
Further, as the exclusive area sensor is not mounted with an on-chip micro lens, the aperture is low and the light-receiving quantity is insufficient, with a low S/N ratio.
It is, therefore, an object of the present invention to provide a focus detector that can secure a sufficient light-receiving quantity to have an improved S/N ratio and an improved focus detection precision, with low cost.
It is a first object of the present invention to provide a focus detector for an image pick-up lens, the focus detector comprising:
a condenser lens disposed near a predetermined focusing surface of the image pick-up lens;
a brightness diaphragm disposed at the rear of the condenser lens, and having a pair of apertures;
an image re-forming optical system of a telecentric type disposed at the rear of the brightness diaphragm; and
a photoelectric converter including photoelectric conversion elements for receiving an image formed by a beam flux passed through the image re-forming optical system.
It is a second object of the invention to provide a focus detector or a distance-measuring device including a detection optical system that guides a beam flux of an image picked-up object onto at least a pair of brightness diaphragms and an image-forming lens, and forms images on light-receiving surfaces of photoelectric conversion elements disposed at the rear of the image-forming lens, wherein
a correction lens for locating an injection pupil for receiving an incident beam onto the light-receiving surface of the photoelectric conversion elements at a substantially infinite distant position, is provided between the image-forming lens and the light-receiving surface of the photoelectric conversion elements.
It is a third object of the invention to provide an automatic focusing camera, comprising:
photoelectric conversion elements;
a detection optical system that includes a pair of brightness diaphragms and a lens disposed at positions along an image-splitting direction, for forming an image of an image picked-up object on the light-receiving surface of the photoelectric conversion elements disposed at the rear of the lens by receiving a beam flux on this surface; and
a controller for controlling an automatic focusing of an image based on an output signal of the photoelectric conversion elements, wherein
the lens corrects a main beam of a beam flux incident to the light-receiving surface of the photoelectric conversion elements to be perpendicular to the light-receiving surface.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.